HMA Pavement Performance and Durability

It has long been argued that at densities higher than approximately 92 percent (air void contents lower than 8 percent), a hotmix asphalt mixture is impermeable to water. However, as densities become lower (air void contents higher) than this, small decreases in the density can yield exponential increases in permeability. The objectives of this study were to better understand the increases in hot-mix asphalt pavement performance and durability that can be gained by increasing the initial pavement density and to better quantify the inter-relationship among pavement density, permeability, and moisture-induced damage. The long-term performance and durability of four hot-mix asphalt mixtures at four different air void contents were evaluated with the dynamic modulus and beam fatigue apparatus. The mixtures differed in both aggregate size and gradation. In order to evaluate durability effects, performance tests were performed on unconditioned, moisture conditioned and ovenaged samples. The results indicate that density (air void content) is a significant factor in the performance and durability of hotmix asphalt mixtures. Its effects vary with aggregate size and gradation, but increases in mixture density (reductions in air voids content) produce improvements in the dynamic modulus (reduction of rutting potential) and fatigue life of a mixture. Further, the fatigue life appears to be less sensitive to density (air voids content) than to moisture damage.